Aero Injector Fine Tuning
Posted: Sun Jun 11, 2023 8:41 pm
by BRS
I posted this as an email to the sonex tech email. Thought I’d post here to see how many different responses I can get…
Background:
I have the 32mm AeroInjector and stock needle on my Revmaster R2300. I have it adjusted so that on climb-out (3200 rpm) I’m flowing about 6.6 gph and the engine feels to be running fine at this current setting WOT. A 1/4 turn leaner and the engine stumbles on take-off.
At cruise (2700-3000 rpm) I lean to about 4.5 gph. At idle I need to lean much more for a smooth idle.
Problem:
If I am at full mixture and pull back to idle the engine is too rich and sometimes dies (on ground). I don’t dare go full rich and idle when on short final. However, to be prepared for a possible go-around I want to be able to do just that (full-rich/idle) while on short final.
Question:
Is there another needle, if so which one, that would lean out my idle rpms yet still allow the same fuel flow at WOT that I have now?
Thank you!
-brs
PS. Don’t ask about EGT’s as I’ve given up on getting meaningful data from my MGL probes and display. Could be I drilled the probes too far from the heads.
Re: Aero Injector Fine Tuning
Posted: Mon Jun 12, 2023 2:56 am
by NWade
Are you sure the issue is “too rich” at idle?
Have you looked at your fuel flow when you pull back to idle and noticed whether it ever goes to zero or near-zero?
And do you have a gascolator or un-insulated fuel lines in the engine bay?
Because a far more common issue in the Sonex is “the burps”, which are vapor bubbles in the fuel line that can cause the engine to stall at idle or near-idle throttle settings during ground-runs or when landing after the engine bay gets hot.
Everything connected to the fuel system (the carb, the fuel lines, a fuel flow sender, etc) all conduct heat back into the fuel system when they get hot.
—Noel
Re: Aero Injector Fine Tuning
Posted: Mon Jun 12, 2023 8:16 am
by XenosN42
What is your idle RPM?
Re: Aero Injector Fine Tuning
Posted: Mon Jun 12, 2023 9:28 am
by BRS
XenosN42 wrote:What is your idle RPM?
Ha, I thought (after hitting post) someone would ask that. With the over-rich idle mixture, as I have, obviously it’s too low else it would not die. I think its in the range of 700 RPM, however when I agressively ground lean, it goes up to something line 1300 RPM. Today I’ll warm it up and get the exact numbers.
However, I feel that bumping up the RPM to fix an overly rich mixture is a ‘FIX’ that should be considered after doing what is possible to have good fuel metering. It might come to that. But then the side-effect is possible fouled plugs unless I lean at idle. This bring me back to…
Re: Aero Injector Fine Tuning
Posted: Mon Jun 12, 2023 10:04 am
by Bryan Cotton
My Aerovee will idle less than 500 when it is warm. It doesn’t sound happy but doesn’t quit. This is handy for landing as you can really get all the power out on final. I like to keep it at 900+ for normal operations. 1300 when leaned sounds too high!
Re: Aero Injector Fine Tuning
Posted: Mon Jun 12, 2023 3:34 pm
by karmarepair
I’m following Jeff Schultz http://www.sonex604.com/aerocarb_thoughts.html and using a 2.5 needle.
It’s worth remembering this fuel system does NOT like rapid throttle opening. It will always lean out if the throttle is rapidly opened, at a given mixture setting. So on short final, PERHAPS a leaned idle is a good thing. Go around, both knobs in, as slowly as your adrenal gland will allow. Detonation on full throttle is what we really want to avoid.
Re: Aero Injector Fine Tuning
Posted: Mon Jun 12, 2023 4:28 pm
by Onex107
I did a lot of research on AeroInjector needles. The three I received with the unit where numbered 2, 21/2, and 3.
The higher the number the more the taper angel increases. It’s just a few minutes of angle but makes a big change. What I found was that the sweet spot on the needle for wot was at a thickness of approx. .080, no mater what the needle number was. And the sweet spot on the needle for idle is very near the beginning of the taper. So the problem is getting the idle sweet spot in the right position after wot is set. I think your problem is the same as mine was with the lower number needles, the lower angle sets the two sweet spots further apart. I ended up with a #3 needle which when set for wot allowed the engine to idle without a mixture change. I took off with the mixture set about halfway out. I leaned a little more at cruise for economy. Exhaust gas temp. 11-1200. I landed, taxied, and never touched the mixture again until the next flight.
Re: Aero Injector Fine Tuning
Posted: Mon Jun 12, 2023 6:10 pm
by tps8903
The EGTs matter. They aren’t meant to be absolute values however. You can still use the relative info for tuning, which is what they are meant for.
If I’m reading your post correctly, full rich on TO gives you 6.6gph, but a 1/4 turn out on a vernier mixture causes the engine to stumble. If that’s the case, I believe you are too lean. I can TO with half mixture, albeit with reduced power (38") with the Aerovee Turbo. I only know that because I did it by accident. As soon as I went full rich before rotation the MAP went to 41".
I also believe full rich should give you more than 6.6gph. I don’t have a fuel flow sensor, but I believe it should be over 7.0gph if not 8gph. Someone else here might chime in. At the end of the day you can always lean, but you can’t go higher than full rich.
A lower needle number will give you what you look for. I went to 2.5 to give a better idle mixture. As mentioned above, I still lean almost all the way out for ground ops, I might have 1/4" left to cutoff.
Re: Aero Injector Fine Tuning
Posted: Mon Jun 12, 2023 7:39 pm
by Area 51%
I had to buy a jeweler’s file and “customize” the needle before I got any satisfaction.
I truly believe you are either blessed with an Aeroinjector with a small orifice, or damned with an oversized hole. In any event, the ramp on the needle is the key.
Happily edge finishing parts here for Chett 2.0 @Area 51%
Re: Aero Injector Fine Tuning
Posted: Tue Jun 13, 2023 12:14 am
by BRS
Wow, lots of responses. Some helpful some not so, but all appreciated.
The 1/4 turn I referenced was on the needle adjusting leaner. No matter.
As promissed I went out and checked the idle (with intensionality and focus). It was not as I had stated. It was more like 870 Lean - 700 to dead on rich. So I guess I’m a bit thick headed sometimes but I did go fly then upon landing, while at full rich, I set and locked the throttle at 1000 rpm and shutdown. Then I reset the idle screw to where the slide was. After, I went flying again and things were much better. Idle is richer than I want but it’s steady and not dying. Only problem was upon landing the idle really seemed to be closer to 1100. Boy did this cause a float issue. I’ll work on getting it closer to 900. If I can get the mixture better I’d like to get the idle to 800.
I get confused when I try to visualize the needle taper, slide & orfice. Usually, in my head, I end up thinking of the narrow end of the needle being for idle, which it’s not. Any hoo, after a good night sleep, I’ll re-read some of the responses.
Re: Aero Injector Fine Tuning
Posted: Tue Jun 13, 2023 8:25 am
by XenosN42
BRS wrote:
Ha, I thought (after hitting post) someone would ask that. With the over-rich idle mixture, as I have, obviously it’s too low else it would not die. I think its in the range of 700 RPM, however when I agressively ground lean, it goes up to something line 1300 RPM. Today I’ll warm it up and get the exact numbers.However, I feel that bumping up the RPM to fix an overly rich mixture is a ‘FIX’ that should be considered after doing what is possible to have good fuel metering. It might come to that. But then the side-effect is possible fouled plugs unless I lean at idle. This bring me back to…
900 RPM is about right. 700 is too low, especially for a new engine. My engine is broken in, and I probably could idle at 700, but why would I? The chances of the engine quitting are too high.
Re: Aero Injector Fine Tuning
Posted: Tue Jun 13, 2023 10:42 am
by BRS
NWade wrote:Are you sure the issue is “too rich” at idle?
Have you looked at your fuel flow when you pull back to idle and noticed whether it ever goes to zero or near-zero?
And do you have a gascolator or un-insulated fuel lines in the engine bay?
—Noel
This is thread-drift bate, but I’ll bite.
Yes, I’m sure it’s mixture and not hot lines as the condition is constant whether I’ve just started the engine and it slightly warmed or if I just landed. My lines are all well insulated though I do have a gascolator. About the gascolator, I’ve thought of removing it several times just because it is so hard to get to. But, call me old school, I want a low fuel point to check for water. Even though I’m hangarared and use 100LL. Hold over from having rented cessnsas for many years. I’d rather like to install a low sump in the fuel tank since it has such a perfect location but don’t want to introduce the fuel-in-cabin possibility.
OK, back to our regularly scheduled program…
Re: Aero Injector Fine Tuning
Posted: Tue Jun 13, 2023 10:45 am
by BRS
karmarepair wrote:It’s worth remembering this fuel system does NOT like rapid throttle opening.
Yes, having flown fuel injected engines for the past 10 years, going back to a carb was a bit of adjustment in this regard. Don’t even have an accelerator pump on this thing! Modern Stone Age.
Re: Aero Injector Fine Tuning
Posted: Tue Jun 13, 2023 10:57 am
by Bryan Cotton
I found this cool picture on another thread:
I assume you remember it! It would seem the #3 needle gives a quicker change from rich to lean. Isn’t this what you were looking for?
Also, fwiw, I can move my throttle pretty quickly and the engine is not unhappy.
Re: Aero Injector Fine Tuning
Posted: Tue Jun 13, 2023 10:58 am
by BRS
Onex107 wrote:…
The higher the number the more the taper angel increases… What I found was that the sweet spot on the needle for wot was at a thickness of approx. .080, no mater what the needle number was. And the sweet spot on the needle for idle is very near the beginning of the taper. So the problem is getting the idle sweet spot in the right position after wot is set. I think your problem is the same as mine was with the lower number needles, the lower angle sets the two sweet spots further apart. I ended up with a #3 needle which when set for wot allowed the engine to idle without a mixture change. I took off with the mixture set about halfway out. I leaned a little more at cruise for economy. Exhaust gas temp. 11-1200. I landed, taxied, and never touched the mixture again until the next flight.
This was most helpful, 1X107. When I think about the taper my brain want’s to think of the thin end as idle. Which really get things confused. I’ll have to give this some thought and take a close look at those needles while in the carb. This would be so easy if the cowl did not have to come off for each little adjustment.
On another note, does anyone have a chart of full rich fuel-flows for their great-running Aerovee (or revmaster)?
Re: Aero Injector Fine Tuning
Posted: Tue Jun 13, 2023 11:13 am
by BRS
Bryan Cotton wrote:I found this cool picture on another thread:
…pic removed…
I assume you remember it! It would seem the #3 needle gives a quicker change from rich to lean. Isn’t this what you were looking for?..
Ha! Thanks Bryan for bringing that image back. I looked just now for the original, seems to be long gone. Funny, there have been so many twists & turns on this sonex project that I’ve now come full circle and barely recognise the starting point.
Re: Aero Injector Fine Tuning
Posted: Tue Jun 13, 2023 8:40 pm
by BRS
Well I’m encouraged. This afternoon I swapped out #2 needle for #3. I had thought it might be too lean but the ground run seemed to indicate it will be close to spot-on once I get things adjusted better. Here is what I found while running (tied down).
Static RPM WOT 3180 at a whopping 8gph. It was smooth running and took acceleration well.
Static idle at full-rich was about 900 rpm then later 800 after WOT runup.
Static idle mixture Leaned was 1000 rpm+. I had not made any idle speed adjustments from before.
So as long as I get a rise when leaning at idle I think I’m good.
Before installing the #3 needle I marked each needle at .080" and at the end of the taper at the idle side.
Re: Aero Injector Fine Tuning
Posted: Wed Jun 14, 2023 9:51 am
by Onex107
Now you’ve got it. As you can see, the two “sweet spots” get closer together. I don’t know what the slide movement distance is, but the object is to get them both within the movement length so they end up in the proper position when the slide is closed. I found that the lower number needles, when adjusted for wot, left the idle sweet spot outside the idle position and I had to lean the mixture almost to cutoff to not stall the engine by being too rich at idle.
I even calculated and graphed the aeria of the slide opening, as it opened, to see if it wasn’t linear. And it is. That wasn’t the problem,
Re: Aero Injector Fine Tuning
Posted: Wed Jun 14, 2023 1:59 pm
by Onex107
In regards to the gascolator. I found that I could not insulate the unit adequately, so I eliminated it as per Sonex. If the fuel system is as per plans, it is downhill all the way from the tank to the AeroInjector. So, if any water is in the tank, it will be at the AeroInjector right away. In support of that, after 20 years of flying a Cessna I never saw/tested any water. And, I didn’t religiously fill the tanks after flying. If you fly often enough condensation doesn’t have time to happen.
Re: Aero Injector Fine Tuning
Posted: Thu Jun 15, 2023 6:56 am
by tps8903
Good job. Looks like you are getting the 8gph I mentioned and a good idle.
Like the other poster I too deleted the gascolator, I was apprehensive to do so, but it has worked out great. No burps. I also insulated the 12" of fuel line I do have post firewall with fiberglass wrap and then gold foil wrap.
